Synthesis and properties novel polyurethane-hexafluorobutylmethacrylate copolymers

Guichang Jiang • Xinlin Tuo • Dongrui Wang •

Qiang Li

Received: 23 November 2011 / Accepted: 30 April 2012 / Published online: 13 May 2012

� Springer Science+Business Media, LLC 2012

Abstract Novel physically crosslinked polyurethane-

hexafluorobutyl methacrylate (PU-M) copolymers were

prepared by the macroiniferter-controlled radical polymeri-

zation method. The chemical structures of the PU-M

copolymers were characterized by FT-IR, 1H-NMR, GPC,

DSC, and XPS. The self-assembly and surface properties of

the PU-M copolymers have been investigated. The results

revealed that PU-M copolymers have good hydrophobility,

so the hydrophobility of polyurethane could be easily

adjusted by controlling the content of the hydrophobic vinyl

monomers. The mechanical evaluation shows that PU-M

copolymers exhibit good mechanical properties. The effects

of the fluorine content on the surface properties and self-

assembly of the PU-M copolymers were investigated. The

morphology of the PU-M copolymers’ self-assembly was

observed by transmission electron microscopy (TEM) and

scanning electron microscopy (SEM), and the mechanism of

self-assembly was investigated. Antimicrobial property of

the chlorinated PU-M copolymers against both Escherichia

coli and Bacillus subtilis bacteria was examined and showed

increase compared to that of pure polyurethane.

1 Introduction

Polyurethanes (PU) have been utilized extensively for a

variety of biomedical applications such as cardiac assist

devices, catheters, and in orthopedic applications.

Although polyurethanes are being increasingly used in

biomedical devices [1], the long-term biostability of

polyurethanes is still major problem for its in vivo appli-

cation. Fluorinated polyurethane, which combines the

properties of fluorinated polymer and polyurethane, has

proven to be an important material for applications in areas

such as coatings and implantable devices. Some researches

have demonstrated fluorinated polyurethane has excellent

oxidative stability, good chemical resistance, low coeffi-

cient of friction, good stability against hydrolysis and good

compatibility with blood in biomedical applications [2–6].

Moreover, incorporation of fluorine into polyurethane can

effectively improve the biostability of polyurethane [7, 8].

Several approaches to the introduction of fluoro-group

into polyurethane have been reported [9, 10]. Most of the

synthesis methods focus on the incorporation of fluoro-

containing hard segments, chain extenders into polyurethane

by polymerization. For example, several researchers utilized

fluorinated diisocyanate as hard segment to obtain new

fluorinated polyurethane [11, 12]. Kajiyama synthesized

fluorinated polyurethane by using various fluorinated diols

and studied their surface properties [13]. Taylor et al. [14]

mixed fluorine-containing polyurethane with base polyure-

thane to improve the surface properties, biocompatibility,

and biostability of the base polyurethane. These fluorinated

polyurethanes however have showed some disadvantages in

bulk or surface properties. For instance, the hard segments

are not easy to migrate to surface for the structure restriction

which results in the undesirable surface properties. End-

capping with fluorinated chain would decrease the molecular

weight of the fluorinated polyurethane and damaged the

fluorinated polyurethane mechanical properties. It is difficult

to synthesize the fluorinated polyurethane with desired

molecular weight distribution and molecular weight. The

G. Jiang (&)

Tianjin University of Science and Technology, 300222 Tianjin,

China

e-mail: wangziqing1978@163.com

G. Jiang � X. Tuo � D. Wang � Q. Li

Laboratory for Advanced Materials, Department of Chemical

Engineering, Tsinghua University, 100084 Beijing, China

123

J Mater Sci: Mater Med (2012) 23:1867–1877

DOI 10.1007/s10856-012-4670-y

controlled polymerization methods allowed the design of

tailored polymers with a desired composition and molecular

weight distribution [15]. One of the controlled polymeriza-

tion methods that could employ polyurethane is the mac-

roiniferter technique [16, 17].

This investigation indicated that the polyurethane-hex-

afluorobutyl methacrylate (PU-M) copolymers can be

prepared by the macroiniferter-controlled radical poly-

merization method [18]. The macroiniferter-controlled

radical polymerization has emerged as general method for

producing polyurethane. This investigation also showed

that the PU-M copolymers were capable of forming fluo-

rine-rich hydrophobic surfaces. The macroiniferter-con-

trolled radical polymerization was proposed by Otsu [17].

Macroiniferter is an initiator, which induces radical poly-

merization by initiation, propagation, primary radical

termination and transfer to initiator. The macroiniferter-

controlled radical polymerization is acted by the insertion

of the monomer into the macroiniferter bond. The polymer

made via a macroiniferter has a capacity to initiate poly-

merization of vinyl monomer [19]. The process of poly-

merization of vinyl monomer with polymer (synthesized

from macroiniferter) is called a macroiniferter radical

polymerization. However, polyurethane-hexafluorobutyl

methacrylate (PU-M) copolymers obtained via the macro-

iniferter-controlled radical polymerization have not been

reported so far. Previously, Radhakrishnan et al. used this

method to successfully synthesize polyurethane-poly-

vinylbenzyl chloride copolymers [18] and polyurethane-

polyacrylic acid copolymers [20].

In the present investigation, we researched the macroi-

niferter approach to synthesize novel polyurethane-hexa-

fluorobutyl methacrylate (PU-M) copolymers and report

their characterization and properties. The structure of the

novel PU-M was characterized by nuclear magnetic reso-

nance (1H NMR), gel permeation chromatography (GPC),

FT-IR, DSC, and XPS. The hydrophobic surface property

of polyurethane-hexafluorobutyl methacrylate (PU-M)

copolymer films with different hexafluorobutyl methacry-

late content was measured with the standard sessile drop

technique with a Dataphysics contact angle meter OCA-20.

The mechanical properties of the PU-M were measured on

a universal testing machine (GT-TS-2000, Taiwan), and

biocidal activity was examined by using a modified version

of AATCC-100 test. The morphology of the PU-M

copolymers’ self-assembly was observed by scanning

electron microscopy (SEM) and transmission electron

microscopy (TEM). The effects of the hexafluorobutyl

methacrylate content on the surface properties and

mechanical properties of these PU were investigated.

2 Experimental section

2.1 Materials

Methylethylketone (MEK) and dimethylformamide (DMF)

(Chemicals, Beijing, China) were distilled at a reduced

pressure of 26 kPa, and the middle fraction was stored at

4 �C until used. Poly(tetramethyleneoxide) glycol (PTMO,

Mw = 1,000) (Sigma–Aldrich, MO, USA) was dried at

90 �C and reduced pressure until it was bubble free. 4,

4-Diphenylmethane diisocyanate (MDI) (Sigma–Aldrich,

MO, USA) was purified by hot filtration, whereas 2-pro-

panol, glacial acetic acid, dibutyltin dilaurate (DBTDL),

hexafluorobutyl methacrylate (HFM) and benzophenone

(Chemicals, Beijing, China) were used as received. All

other precipitating solvents (Chemicals, Beijing, China)

were also used as received.

2.2 Preparation of tetraphenyl-1,2-ethanediol

Benzophenone (18.2 g; 0.1 mol) and sixfold molar excess

isopropyl alcohol in the presence of glacial acetic acid

(2 mL) were mixed. The mixture was assembled in a

beaker and exposed to UV light. Tetraphenyl-1,2-ethane-

diol (TPED) precipitated as it was formed. TPED was then

filtered and recrystallized from acetic acid and stored at

5 �C until used (Scheme 1). (Yield: 89 %; Purity: 95 %;

M = 366.46 g/mol). IR (Fig. 1A): 3,500–3,550 cm-1

(OH), 3,010 cm-1 (phenyl). 1H NMR (The spectrum was

taken in CDCl3, Fig. 2): d = 3.02 ppm (a, OH),

7.10–7.40 ppm (b, c, d, e, f, H, phenyl).

2.3 Preparation of polyurethanes (PU)

A 250 mL glass reactor equipped with a mechanical stirrer,

heating element, a charging and sampling port, a

Scheme 1 Synthesis of TPED

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123

condenser, and a nitrogen inlet and outlet was charged with

PTMO 1000 (50 % solution in MEK) and 4,4-diph-

enylmethane diisocyanate (MDI) in 1:2 molar ratio. The

mixture was heated to 65–75 �C and allowed to react for

2.5 h. After 2.5 h, the temperature was reduced to 25 �C,

and stoichiometric amounts of tetraphenyl-1,2-ethanediol

(TPED) and 0.2 % dibutyltin dilaurate (DBTDL) (based on

the isocyanate content) were added and allowed to react

with the isocyanate (–NCO) for 20 h. Samples were fre-

quently taken for FTIR analyses and reaction was allowed

to proceed until the peak related to the isocyanate

(2,265 cm-1) disappeared from the FTIR spectrum. The

polyurethanes (PU) were precipitated by pouring it into a

water–methanol mixture (1:3 v/v) and dried at 30 �C in a

vacuum oven (Scheme 2). Molecular weight: 4.62 9

104 g/mol (Mn). 1H NMR (The spectrum was taken in

CDCl3, Fig. 3): d = 1.61 ppm (b, CH2, PTMO), 3.40 ppm

(c, CH2O, PTMO), 3.80 ppm (d, CH2, MDI), 4.15 ppm (a,

OCH2, PTMO), 7.10–7.40 ppm (e, H, phenyl). IR

(Fig. 1B): 3,307 cm-1 (NH), 2,945 cm-1 (aliphatic stretch),

2,857 cm-1 (aliphatic stretch), 1,735 cm-1 (C=O), 1,100 cm-1

(C–O–C).

2.4 Preparation of PU-M copolymers

HFM (6.5 g) and PU (5 g; 20 % in DMF) were charged in a

round-bottom reaction flask equipped with heater and a

magnetic stirrer. Nitrogen was bubbled through the reactor

to remove dissolved oxygen. The reaction flask was heated to

75–85 �C to initiate the reaction and obtain PU-M. The

samples were taken at regular time intervals (24 h), chilled

in ice-cold water to terminate the polymerization, and pre-

cipitated in cold methanol. The PU-M copolymers were

dried at 50 �C in a vacuum oven. The reaction scheme for

the synthesis of PU-M is shown in Scheme 2. Molecular

weight: 6.98 9 104 g/mol (Mn). 1H NMR (The spectrum

was taken in CDCl3, Fig. 4): d = 1.61 ppm (b, CH2,

PTMO), 3.40 ppm (c, CH2O, PTMO; g, CH2, HFM),

3.80 ppm (d, CH2, MDI), 4.15 ppm (a, OCH2, PTMO),

7.10–7.40 ppm (e, H, phenyl). New peaks, which were not

observed for the PU, corresponding to the CHF (f) aliphatic

protons of the HFM, and CH2 (i) aliphatic protons adjacent to

the CH3 group of HFM, were observed at 3.95 ppm and

2.0 ppm, respectively. The peak related to the CH3 (h) ali-

phatic protons from HFM also appeared between d = 0.8

Fig. 1 FTIR spectra of A: TPED (OH peak at 3,500–3,550 cm-1)

and B: (a) PU (NH peak at 3,307 cm-1), (b) PU-M (FC peaks at

1,070 cm-1) (F2C and F3C peaks between 1,020 and 1,350 cm-1)

Fig. 2 1H NMR spectrum

of TPED

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123

and 1.0 ppm. IR (Fig. 1B): 3,307 cm-1 (NH), 2,945 cm-1

(aliphatic stretch), 2,857 cm-1 (aliphatic stretch), 1,735 cm-1

(C=O), 1,100 cm-1 (C–O–C), 1,070 cm-1 (FC), 1,020–

1,350 cm-1 (F2C and F3C).

2.5 Characterization

Nuclear magnetic resonance (1H NMR) spectra in chloro-

form-d3 (CDCl3) were recorded on a JEOL JNM-ECA600

NMR spectrometer. Infrared spectra were measured using a

Nicolet 560-IR spectrometer by incorporating the sample

in a KBr disk. The molecular weights and their distribu-

tions of the polymers were determined by gel permeation

chromatography (GPC) utilizing a Waters model 515 pump

and a model 2410 differential refractometer with three

styragel columns HT2, HT3, and HT4 connected in a serial

fashion. THF was used as the eluent at a flow rate of

1.0 mL/min. Polystyrene standards with dispersity of

1.08–1.12 obtained from Waters were employed to cali-

brate the instrument. The DSC studies of PU and PU-M

were carried out using a DSC 2910 (TA instrument, New

Castle, DE). The PU-M and PU were dried in a vacuum

oven at 50 �C for 28 h before use. The PU-M and PU

weighing between 5 and 15 mg were sealed in a DSC pan

and quenched to -70 �C. The samples were then left to

equilibrate for 15 min and heated to 200 �C at a rate of

5 �C/min. XPS was carried out on an XSAM-800 electron.

The spectrometer was equipped with a MgKa achromatic

X-ray source (20 kV, 10 mA), and take-off angle of 30�was used with X-ray source. The sample for XPS was

prepared by casting the polymer onto a clean glass disk

from 10 % (w/w) mixed solution of ethyl acetate and

ethanol. The disk was put into an oven at 60 �C for 12 h

and 60 �C for 12 h under vacuum.

2.6 Mechanical properties experiment

The mechanical properties of the PU-M films were mea-

sured on a universal testing machine (GT-TS-2000,

Taiwan) according to GB528-76 with a tensile speed of

300 mm/min at 25 �C to obtain the tensile strength and the

breaking elongation. The samples were casted from THF

Scheme 2 Synthesis of PU-M

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solutions and shaped to dumbbell products. The thickness

and width of the specimens were 3.0 and 3.2 mm,

respectively. The length of the sample between the two

pneumatic grips of Testing Machine was 12 mm. Five

measurements were conducted for each sample, and the

results were averaged to obtain a mean value.

2.7 Surface properties experiment

The PU-M films were prepared by spin-coating method

(The PU-Ms were dissolved in THF and cast to a thickness

of *0.5 mm on Teflon substrates. Films were peeled from

the substrates after being dried in a vacuum oven at 60 �C).

Fig. 3 1H NMR spectrum

of PU

Fig. 4 1H NMR spectrum

of PU-M

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The contact angles of water on the film surfaces were

measured with the standard sessile drop technique by using

a Dataphysics contact angle meter OCA-20. A water drop

(2 lL) was made on the tip of a syringe and placed on a

surface by moving the sample stage vertically until contact

was made between the water drop and the surface. An

image of the droplet was taken through a CCD camera and

enlarged on computer screen. Contact angles were obtained

by using the equipped software based on Young–Laplace

fitting method. The contact angles reported in this paper are

advancing contact angles. Experimental errors were esti-

mated from the measurements on 10–12 droplets placed at

different sample locations.

2.8 Antimicrobial properties experiment

Antimicrobial properties of the PU-M films were examined

by using a modified version of AATCC-100 test. A 1 lL

drop of a bacterial suspension was placed on the coated

glass microscope slide surface. An identical glass micro-

scope slide was used to sandwich the drop. A 100 mL

beaker (a convenient mass) was placed on sandwich to

ensure contact. The bacteria were kept between the glass

microscope slides for a predetermined time, typically

30–60 min. The glass microscope slides were separated

and all bacteria were removed via vortexing in aqueous

3 wt% sodium thiosulfate solution for 1 min. A 100 lL

aliquot of the vortexed supernatant sodium thiosulfate

solution was plated on nutrient agar plate (designated as

plate-0). Two serial tenfold dilutions were performed. All

plates were incubated at 37 �C for 24 h. Tests on both the

chlorinated PU-M films (experimental) and the PU films

(control) followed the same procedure.

3 Results and discussion

3.1 Preparation of PU-M

Controlled free radical polymerization is an important

means for the synthesis of block copolymers with the

desired molecular weight [20, 21]. In this paper, we first

synthesized PU-M by controlled radical polymerization

using a polyurethane macroiniferter. Table 1 summarizes

the compositions of the different PU-M with the corre-

sponding molecular weight. Figure 1 shows the FTIR

spectra of TPED, PU, and PU-M which demonstrate the

presence of the expected functional groups. The FTIR

spectrum of TPED shows a broad peak between 3,550 and

3,500 cm-1 related to the OH peak. For the PU, the peak at

3,307 cm-1, a characteristic peak of the urethane amide

bond appeared while the OH peak observed for TPED

disappeared indicating that the reaction was completed. In

the FTIR spectrum of PU-M, a novel peak at 1,070 cm-1

related to the FC stretching (from HFM) is observed,

whereas the peak at 1,735 cm-1 related to carbonyl group

is increased. This demonstrates the successful incorpora-

tion of HFM to the polyurethane backbone during copo-

lymerization. The band observed at 1,103 cm-1 (F2C

stretching) indicates the presence of fluorocarbon chains

in these PUs. As expected, the intensity of the F2C

absorption peak depended on the concentration of the

fluorocarbon chain. The urethane carbonyl stretching

vibrations appeared in the range from 1,671 to 1,771 cm-1.

For the HFM, carbonyl absorption peaks occurred at 1,702

and 1,742 cm-1, in addition to those at 1,686 and

1,723 cm. The first two peaks result from the fluorocarbon

chain units inducing shifts on the hydrogen-bonded and

free carbonyl groups, respectively. The latter two peaks

represent the hydrogen-bonded and free carbonyl groups,

respectively, of the soft segments of the PU. Yoon and

Ratner [22] reported that the absorptions of carbonyl

groups linked to fluorocarbon chain units are shifted to

higher frequencies, relative to those linked to soft segment

units, presumably because of variations in the bonding

electron densities of the carbonyl groups. IR (Fig. 1B):

3,307 cm-1 (NH), 2,945 cm-1 (aliphatic stretch), 2,857 cm-1

(aliphatic stretch), 1,735 cm-1 (C=O), 1,100 cm-1 (C–O–C),

1,070 cm-1 (FC), 1,020–1,350 cm-1 (F2C and F3C).

Figure 2 shows the 1H NMR spectrum of TPED. The OH

protons from TPED appeared at d = 3.02 ppm, and the

peaks related to the aromatic protons appeared between

d = 7.10 and 7.40 ppm. Figure 3 shows the 1H NMR

spectrum of PU. The aromatic protons between d = 7.10 and

7.40 ppm are from TPED and 4, 4-diphenylmethane diiso-

cyanate (MDI) whereas the CH2 protons from MDI are

identified at about d = 3.80 ppm. The aliphatic protons of

polytetramethylene oxide (PTMO), namely CH2, CH2O, and

OCH2 attached to the urethane amide groups are observed at

d = 1.61, 3.40, and 4.15 ppm, respectively.

Figure 4 shows the 1H NMR spectrum of the PU-M.

The 1H NMR spectrum of the PU-M confirms the HFM

Table 1 Molecular weight and molecular weight distribution of

PU-M

Parent

polymeraPercent weight

ratio composition

(%)

Mn (9104) Mw/Mn

PU 100:0 4.62 2.81

PU-M20 80:20 5.73 2.03

PU-M35 65:35 6.16 1.75

PU-M45 55:45 6.65 1.69

PU-M55 45:55 6.98 1.48

a HFM content calculated based on conversion and yield during

synthesis

1872 J Mater Sci: Mater Med (2012) 23:1867–1877

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polymerization into the polyurethane backbone. New

peaks, which were not observed for the PU, corresponding

to the CHF (f) aliphatic protons of the HFM, and CH2

(i) aliphatic protons adjacent to the CH3 group of HFM,

were observed at 3.95 ppm and 2.0 ppm, respectively. The

peak related to the CH3 (h) aliphatic protons from HFM

also appeared between d = 0.8 and 1.0 ppm. In the FTIR

(Fig. 1B) spectrum of PU-M, a new peak between 1,010

and 1,120 cm-1 related to the FC stretching (from HFM) is

observed, whereas the peak between 1,671 and 1,761 cm-1

related to carbonyl group is increased. This confirms the

successful incorporation of HFM to the polyurethane

backbone. Also, XPS was used to verify the result. The

present of a strong signal attributable to fluorine atoms (F

1S: 683 eV) is clearly evident in XPS survey spectra of the

sample made by purified PU-M (see Fig. 5).

3.2 Surface properties of PU-M

The water contact angles, which are indicative of the

hydrophobic properties of the samples, are presented in

Table 2. As the HFM content is increased, the polymers

showed improved hydrophobicity, as evidenced by the

increase in contact angles, due to the generation of

hydrophobic HFM chains. Since the only hydrophobic

component of the present samples is HFM, the water

contact angles data indicate the successful incorporation of

the monomer via the macroiniferter chemistry.

3.3 Thermal analysis of PU and PU-M

Figure 6 shows the thermal transitions of PU and PU-M.

Both PU-M and PU show two Tgs; the lower temperature

shows the soft segment Tg and the higher temperature

shows the hard segment Tg. The lower Tg is related to the

polytetramethylene oxide soft segment and is higher than

the Tg of pure polytetramethylene oxide (-82 �C) [23],

which suggests the presence of dissolved hard segment

chains. The hard segment Tg for the control PU is observed

at around 128 �C but the incorporation of the HFM block

increased its Tg to 150 �C, presumably due to the presence

of hydrogen bonding between the polyurethane and HFM

segments.

3.4 Mechanical properties of PU-M

Table 3 shows the mechanical properties of the PU-M

materials. All of the PU-M materials show a good

mechanical performance comparison with other fluorinated

PU synthesized [24], especially the breaking elongation. It

is very interesting that the PU-M55 exhibits a maximum

breaking elongation value of 1005.6 %. As is well-known,

an increase of material tensile strength results usually in the

decrease of its breaking elongation for most polymers or

polymer composites. In literature [24], an increasing con-

tent of 1H, 1H, 12H, 12H-perfluoro-1, 12-dodecanediol led

to a significant increase in the tensile strength and to a

Fig. 5 XPS for the PU-M

Table 2 Water contact angles of PU-M

Sample PU PU-M20 PU-M35 PU-M45 PU-M55

Contact anglesa 81 ± 2� 101 ± 2� 110 ± 2� 117 ± 2� 122 ± 2�a Data are expressed as ±SD

Fig. 6 DSC traces of (A) PU: Tg1(-51 �C), Tg2(128 �C) and

(B) PU-M: Tg1 (-46 �C), Tg2 (150 �C)

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123

decrease in the elongation at break of the fluorodiol-

containing PU. However, the tensile strength and the

breaking elongation of the PU-M materials increase

simultaneously in this research. The tensile strength of the

PU-M35 has a value of 897.9 N/cm2. Tensile strength and

breaking elongation reach the minimum value (699.8 N/

cm2 and 689.7 %) when PU-M20, whereas this mechan-

ical performance is still high compared with other PU

samples. When used for biomedical applications, they are

expected to have a much longer life span. The mechanical

performance of the PU-M55 is better than the other

samples. The mechanical evaluation shows that the PU-M

materials exhibit good mechanical properties, especially

breaking elongation, which could be attributed to network

structure and increased molecular weight. It is also

plausible to assume the presence of hydrogen bonding

between the carbonyl of the HFM and the urethane

hydrogen that makes the current biomaterials mechani-

cally strong.

Table 3 Mechanical performance of PU-M

Samples Breaking elongation

(%)

Tensile strength

(N/cm2)

PU Ave.a 509.8 ± 43.2 618.7 ± 57.8

PU-M20 Ave. 689.7 ± 57.3 699.8 ± 68.7

PU-M35 Ave. 831.3 ± 69.8 897.9 ± 98.6

PU-M45 Ave. 909.8 ± 99.6 929.2 ± 103.5

PU-M55 Ave. 1005.6 ± 126.7 1009.7 ± 128.9

a The average number of five films. Data are expressed as ±SD

Fig. 7 SEM images of the

samples (The assembly

of PU-M was investigated by

dissolving the PU-M in

THF:water (80:20, v/v), filtering

and dropping on a glass patch.

After evaporation for 48 h

under ambient conditions, the

samples were observed by

SEM)

Fig. 8 TEM images of the THF: water = 90:10 (1 wt%) sample

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3.5 Assembly behavior of PU-M

The solvent-induced assembly of PU-M was investigated by

dissolving the PU-M in THF:water (80:20, v/v), filtering and

dropping on a glass patch. After evaporation for 48 h under

ambient conditions, the samples were observed by SEM [25,

26]. Figure 7 shows SEM images of the samples, which

show that the polymer creates morphologies that are

microporous or sphere-like (Fig. 7a–c). The average sphere

size was calculated from the SEM picture and the sphere

sizes were homogeneous. The samples have sphere sizes

ranging from 90 nm to 1.2 lm. The quantity of water in the

incorporated solution performs an important role in the

assembly and morphological shifts in the polymers [27]. The

pores vanished and the formation of spheres was observed

with an increased quantity of water in the THF ? water

mixtures (Fig. 7b, c). To investigate the effect of a large

amount of water on the morphology of polymers, the sam-

ples were subjected to a solvent-induced evaporation process

with water/THF ratios up to 50:50. On increasing the amount

of water (THF: water = 65:35), the spheres are distributed at

random on the substrate, and the number of spheres have

decreased to a very great extent as seen in Fig. 7d. For

THF:water = 50:50, the aggregation becomes uncontrolla-

ble, resulting in the vanishing of the spheres [28]. It is

important to mention that the polymer solutions were clear

up to 30:70 of water/THF, whereas large amounts of water

(water: THF = 50:50 and more) rendered the polymer

solutions hazy. Consequently, the amount of water is crucial

in obtaining a good polymer morphology by solvent-induced

self-organization. The samples were also observed by TEM.

The TEM images were obtained from the THF:

water = 90:10 (1 wt%) sample (Fig. 8). The film was pre-

pared by dropping the aforementioned solution onto the top

of a Formvar-coated copper grid. The TEM image of the

sample showed the existence of spheres, which is in

Table 4 Antimicrobial property of PU-M

Challenge Type

gram

Contact

time (min.)

Reduction

(%)

Log

reduction

B. subtilia ? 30 95.5 3.37

60 99.9 3.38

E. colib _ 30 99.8 2.61

60 99.9 2.61

a Average of duplicatesb Average of triplicates

Fig. 9 Sample for chlorinated PU-M (a) and PU (b). The challenge is E. coli and the exposure time is 60 min

Fig. 10 Sample for chlorinated

PU-M (a) and PU (b). The

challenge is B. subtilis and the

exposure time is 60 min

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accordance with that of SEM images. The size of the spheres

ranges from 300 nm to 1.1 lm (Fig. 8). In this study we have

created micron or nanosized materials with good reproduc-

ibility by solvent-induced assembly process, as confirmed by

microscopic techniques of different length scales (SEM and

TEM). It is obvious that the samples showed microporous

morphology when cast from THF and increasing the amount

of water induced the formation of spheres. Furthermore,

depending on the quantity of hexafluorobutyl methacrylate

present in the copolymers, they either appeared as isolated or

aggregated spheres. It is very important to add here that this

is the first time that such a variety of morphologies of porous

membranes and spheres were observed for any type of

fluorinated polyurethane in the literature. In this case, the

assembly during solvent evaporation may arise by nonco-

valent interactions: hydrogen bonding through urethane

linkage.

3.6 Antimicrobial properties

A modified version of the AATCC-100 antimicrobial

testing method was employed. The PU-M copolymers films

were challenged with either E. coli (Gram-negative) or B.

subtilis (Gram-positive) bacteria. The PU films were used

as controls. The results of the AATCC-100 experiments are

shown in Table 4. Calculation of log reduction takes into

account two serial tenfold dilutions prior to culture. In the

cases, there are no surviving bacteria the calculation of

percent kill includes an assumption of one survivor. In this

method, log kill can be estimated as a lower limit. Table 4

exhibits the antimicrobial properties experimentation

results for different strains of bacteria for 30 and 60 min

touch times. Except for B. subtilis (Gram-positive) with

30 min of exposure time, no surviving bacteria were

observed on testing plates. The number of surviving bac-

teria from the control was counted for each antimicrobial

test. Table 4 exhibits also results of the log decrease val-

ues. Within the accuracy of AATCC-100 experimentation

the antimicrobial properties samples executed the same

against both types of bacteria (Figs. 9, 10).

4 Conclusions

Novel PU-M copolymers for biomedical applications were

synthesized using a macroiniferter technique. The structure

of the PU-M copolymers was characterized by 1H-NMR,

FT-IR, GPC, XPS, and DSC. The mechanical evaluation

shows that PU-M copolymers exhibit good mechanical

properties. Antimicrobial property of the chlorinated PU-M

copolymers films against both Escherichia coli and Bacil-

lus subtilis bacteria was examined and showed increase

compared to that of pure polyurethane. This investigation

provides a clear insight into the solvent-induced self-

assembly in the novel PU-M copolymers for the various

morphologies and sizes ranging from micron to nanometer

sized pores and spheres.

Acknowledgments This project was supported by National 863

Foundation of China (No. 2006 AA 02 Z4D4) and the China Post-

doctoral Science Foundation (Nos. 20080430033 and 200902090).

The Project was Supported by The Tribology Science Fund of State

Key Laboratory of Tribology (SKLTKF10B08).

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